Method of producing symmetrical difatty acid diamides

ABSTRACT

The present invention relates to a process of producing symmetrically structured difatty acid diamines by reacting mixtures of fatty acids or their esters with diamines, isolating the symmetrical difatty acid diamides from the reaction mixture by making use of their different solubilities and concentrating them by recrystallisation if necessary. The invention also provides for a process of isolating a fatty acid from a mixture of fatty acids wherein the difatty acid diamides produced in the process of the invention are saponified to yield the corresponding free fatty acid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to Federal Republic of Germany ApplicationNo. P3921342.0, filed Jun. 29, 1989, and International Application No.PCT/EP90/00996, filed Jun. 22, 1990, both of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of producing difatty acid diamides ofsymmetrical composition and/or the corresponding pure fatty acids fromfatty acids or fatty acid esters.

2. Technology Review

Difatty acid diamides are compounds with a wide range of technicalapplications that are used, among other things, as auxiliary materialsin plastics processing, as lubricants, or as fluxing agents for solders.Such difatty acid diamides are chiefly made by reacting activated fattyacid mixtures of commercial oils with diamines. The diamides resultingfrom these kinds of reaction are not uniform compounds in chemicalterms. They are rather mixtures of difatty acid diamides as they formaccording to the various possibilities of combination, depending on thefatty acid composition of the raw materials used. When starting fromnatural fats and oils, which contain three different kinds of fattyacids, mixtures of six different difatty acid diamides thus resultaccording to the rules of combination, some of which are symmetrical,i.e. are composed of two like fatty acid residues, and others areunsymmetrical. Such difatty acid diamide mixtures of heterogeneouscomposition can therefore only be used in cases where heterogeneity isnot troublesome or is even advantageous. In contrast, pure diolecic aciddiamides for example can be used to advantage as lubricating agents forplastics as used, for example, for the sheathing of cables.

Separating fatty acid mixtures usually requires considerable efforts.This is due, among other things, to the structural similarity of thefatty acid molecules to be separated or the reactivity of the frequentlypreset double bonds. Separation is the more difficult higher purity whenpurity is required of the end product. Particular problems arise whenseparating fatty acids of identical chain length which differ only withrespect to the number of double bonds. This applies, for example, to thetechnically very interesting C₁₈ carboxylic acids, stearic acid, oleicacid, linoleic acid and linolenic acid. Isolating oleic acid fromnatural fats is thus very toilsome, because absolute separation fromother saturated and unsaturated fatty acids is extremely difficult toachieve. Accordingly, the classical method of producing pure oleic acidby low-temperature crystallization of the fatty acids of olive oil ortheir methyl esters involves much effort and great losses. However,oleic acid is a very good example by which to demonstrate that a highercontent of this constituent, e.g., in cosmetic products like sun lotion,improves the quality of these products considerably.

SUMMARY OF THE INVENTION

The present invention provides for a process of producing symmetricallystructured difatty acid diamides comprising reacting mixtures of fattyacids or their esters with diamines, possibly in a suitable solvent andwith or without the addition of catalysts and antioxidants; and,separating the symmetrical difatty acid diamides from the resultingreaction mixture by techniques based on differential solubility and, ifdesired, further purifying said diamides by recrystallization. Theinvention also provides for a process of isolating a fatty acid from amixture of fatty acids wherein the difatty acid diamides produced in theprocess of the invention are saponified to yield the corresponding freefatty acids.

DETAILED DESCRIPTION OF THE INVENTION

An object of the present invention was to provide a method by which itis possible to obtain symmetrically structured difatty acid diamides ofsuch great purity that on one hand they are suitable basic materials forproducing high-quality materials such as plastics, as described in thesimultaneously filed patent application U.S. Ser. No. 07/659,317, filedFeb. 28, 1991, and on the other hand can be used as initial substancefor isolating fatty acids that are difficult to obtain otherwise.

According to the invention this object has been fulfilled by a method ofproducing symmetrically structured difatty acid diamides or thecorresponding pure fatty acids, comprising reacting mixtures of fattyacids or their esters with diamines, possible in a suitable solvent andwith or without the addition of catalysts and antioxidants; and,separating the symmetrical difatty acid diamides from the resultingreaction mixture by techniques based on differential solubility and, ifdesired, further purifying said diamides by recrystallization. Thecorresponding free fatty acids are then provided by saponification ofthe separated difatty acid diamides.

Surprisingly it was found that the solubilities and crystallizationrates of saturated, unsaturated and hydroxylated fatty acids in organicsolvents differ much more than those of the corresponding free acids.The solubility is critically dependent on the functional groups withinthe fatty acid molecules and follows some fundamental rules.

It has been found that diamides of fatty acid molecules containing an OHgroup are much less soluble than the diamides of saturated andunsaturated fatty acids. For example, the difatty acid diamidescontaining 12-hydroxystearic acid, which occur in hydrogenated castoroil are practically insoluble even in boiling methanol. Furthermore, thenumber of hydroxyl groups influences the solubility to such an extentthat dihydroxyl compounds such as bis-12-hydroxystearic acid diamidescan be easily separated from those diamide derivatives which containonly a single fatty acid residue with hydroxyl groups. An additionaldouble bond such as for example, in ricinoleic acid, improves thesolubility significantly. It has also been observed that the solubilityof the relevant diamides increases over that of the diamides of thecorresponding saturated fatty acids as a function of the number ofdouble bonds. This makes it easy to separate the unsaturated fatty acidsboth from saturated fatty acids and from fatty acids bearing hydroxylgroups. The differences are so significant that, although the solubilityof fatty acids usually increases with decreasing chain length, evenrelatively short-chained saturated fatty acids like lauric acid, whichoccurs in high concentration in palm kernel oil and coconut butter, canbe easily separated from C₁₈ -unsaturated fatty acids in form of theirdiamides. It has been found further that symmetrically structureddifatty acid diamines have a lower solubility combined with a highercrystallization rate than unsymmetrically structured difatty aciddiamides, provided the respective elements of the diamides are fattyacids with comparable solubility properties. The solubility of diamidescomposed of saturated and unsaturated fatty acids lies between thesolubilities of diamides consisting only of saturated, or only ofunsaturated fatty acids.

Another surprising finding was that overproportionally great amounts ofuniformly composed difatty acid diamides result from oils and fats inwhich one fatty acid predominates in the fatty acid composition. In thisrespect it is irrelevant what kind of fatty acid it is. If, for example,the fatty acid composition contains 50% oleic acid, the resultantdifatty acid diamides include 25% of dioleic acid diamide at the most.If the oleic acid content amounts to roughly 70%, which is the usualconcentration in commercial products, a maximum of 49% dioleic aciddiamide will form. A mixture of difatty acid damides contains about 80%of uniformly structured dioleic acid diamide when triglycerides are usedas initial substance whose fatty acid composition includes 90% oleicacid.

Using the method according to the invention, these findings can beutilized to particularly great advantage for producing symmetricaldifatty acid diamides from fatty acid mixtures in which one fatty acidis highly predominant; on the other hand it is possible at the same timeto concentrate and isolate rare, extraordinary fatty acids. What isparticularly advantageous is that, as is described in the simultaneouslyfiled patent application U.S. Ser. No. 07/659,316, filed Feb. 18, 1991,the reaction with diamines of mixtures of fatty acid esters or fattyacids is not restricted to prepurified fatty acid products, but can alsobe carried out with crude fats and oils, so that the oils of new plantbreeds, for example a new sunflower breed with high oleic acid contentor Euphorbia lathyris whose fatty acid composition contains about 85%oleic acid, can also be processed further. In the latter case theresultant difatty acid diamide mixture contains about 70% dioleic aciddiamide.

Basically, any mixture of saturated, unsaturated and hydroxylated fattyacids and fatty acid esters can be used for the method according to theinvention. Particularly advantageous initial substances are fats andoils of vegetable or animal origin as produced by the usual methods,e.g. cold or hot pressing in worm or screw presses or press extraction.It is advisable that any solid matter that is possibly contained in suchraw initial substances, e.g. wood or plant residues, be removed prior tothe reaction. Those fats and oils are preferred which have aparticularly high content of functional or extraordinary fatty acids.The content of ordinary functional fatty acids should preferably amountto at least 50%, that of extraordinary fatty acids to at least 10%,always related to the total number of fatty acid molecules. Particularlypreferred oils are the oil of Euphorbia lathyris, sunflower oil rich inoleic or linoleic acid acid, in particular the "high-oleic" kind ofsunflower oil, castor oil or hydrogenated castor oil, linseed oil andrapeseed oils, especially rapeseed oil rich in erucic acid, the oil ofJatropha curcas, olive oil or the oil from marine animals such as fishor whale oil. The initial reaction batch may be varied at will, so thatbasically the method can be applied both in the laboratory and at theindustrial scale.

The respective initial substances can be reacted directly with thediamines. Diamines that can be used are, for example, primary andsecondary aliphatic, cyclo-aliphatic, aliphatic-aromatic or aromaticdiamines, preferably with 2-44 carbon atoms. This includes also dimericfatty acids from natural fats and oils for example. Additionalstructural elements or additional functional groups such as ethergroups, amino groups, diamide groupings, ketone groups or sulphonegroups may be arranged between the two amino functions in thehydrocarbon chain or at the cyclo-aliphatic or aromatic residue of thediamines. Preferred diamines are 1,2-diaminoethane, 1,3-diaminopropane,1,6-diaminohexane, 1,8-diaminooctane, piperazine,4,7,10-trioxatridecane-1,13-diamine, 3,3'-diaminodiphenylsulphone,3,3'-dimethyl-4,4'-diaminodicyclo-hexylmethane and commerciallyavailable ether diamines with the structural formula ##STR1## where n isbetween 1 and 2000. 1,2-diaminoethane and 1,6-diaminohexane areparticularly preferable compounds.

The diamines are preferably used in stoichiometric quantities related tothe amino functions and fatty acid residues, but the mixing ratio is notoverly critical, because even at a twofold excess of amino functions thediamides surprisingly still form prior to the monoamides.

If necessary, an appropriate solvent can be used to ensure a homogeneouscourse of the reaction. Non-polar solvents are normally used for this,in particular toluene, xylene or petroleum ether are preferred.

The reaction can occur at temperatures between 20° and 300° C., but thetemperature range between 50 and 200° C. is preferred, because in thistemperature range the reaction time is a reasonable 1 to 6 hours.

As a precaution, the reaction is carried out in a closed system, e.g. anautoclave. It requires no complicated procedure, but an inert gasatmosphere, e.g. of argon or nitrogen, is preferred because thisprovides more protection against undesired side-reactions such asoxidation of the initial substances.

If desired, catalysts such as ammonium chloride or toluene-p-sulphonicacid can be added to the reaction mixture. Biological catalysts such asesterases can also be used at the temperatures suited for these enzymes.Other auxiliary agents and additives like polymerisation inhibitors andantioxidants, e.g. ascorbic acid or glucose, can also be added.

When the reaction is completed the reaction products are separated bysimple or fractionated crystallization and, if necessary, recrystallizedfrom appropriate solvents. Both polar and non-polar substances can beused as solvents. Recrystallization is preferably done with methanol orethanol. A simple washing process, for example with toluene or methylalcohol, is possibly sufficient to obtain pure reaction products Aparticularly preferred method is hot vapour extraction which also permitthe difatty acid diamides to be obtained in crystalline form.

The difatty acid diamides produced by the method according to theinvention are of such purity that their further processing presents noproblem. Therefore, the difatty acid diamides can either be useddirectly as additives, for example, for lubricants, or converted intoother interesting secondary products. As described in the simultaneouslyfiled patent application U.S. Ser. No. 07/659,717, difatty acid diamideswhose fatty acid residues bear function groups such as carbon-carbondouble bonds or OH groups, for example the highly concentrated dioleicacid diamides from the crude oil of Euphorbia lathyris or the highlyconcentrated diricinoleic acid diamides from crude castor oil, can bereacted with appropriate difunctional compounds like diisocyanates andthus constitute new key chemicals for the production of prepolymers,plastics and plastic additives, e.g. for adhesives, sealing materials,foamed plastics, lubricants and a number of other technical auxiliarysubstances. With the usual saponification methods it is also possible toproduce free fatty acids from the difatty acid diamides. These fattyacids can then be derivative or, if they comprise further functionalgroups, may serve as basic or additive substances for plastics.

According to the invention, however, utilizing the differences insolubility of the diamides permits not only the main fatty acidcomponents of the initial substances to be enriched, but when using themethods of the present invention, those fatty acids which are containedin smaller quantities are also automatically concentrated. Bysaponification of the concentrated difatty acid diamide mixtures and, ifnecessary subsequent separation, e.g. by distillation, it is thuspossible to produce fatty acid mixtures whose fatty acid composition isclearly different from that of the initial substances. Taking thepreviously described regularities concerning the solubility of difattyacid diamides into account, the method according to the invention thusmakes it possible to change the fatty acid composition of a giveninitial mixture in a predictable manner, or else, to isolate individualacids that are present only in small quantities.

The easy isolation of symmetrically structured diamides which becomespossible by the method according to the invention increases theindustrial usefulness of oils and fats considerably. The method isparticularly suitable and efficient for separating fatty acids frommixtures in which one fatty acid is highly predominant and forseparating mixtures of the industrially particularly interesting C₁₈fatty acids. Also for the short-chained fatty acids, in particularlauric acid, there is a considerable industrial demand which can besatisfied by the method according to the invention.

Consequently, the invention permits not only the easy synthesis of thosefatty acids and their derivatives that have been hard to obtain so far,but it also makes it possible to produce a great number of new keychemicals that so far could not be utilised in the chemical industrybecause of their difficult availability.

The invention is exemplified in the following examples:

EXAMPLE 1 Reaction of euphorbia oil with 1,2-diaminoethane

100 g euphorbia oil (fatty acid composition: 7% palmitic acid, 2%stearic acid, 84% oleic acid, 3% linoleic acid, 3% linolenic acid) and9.4 g 1,2-diaminoethane are stirred in a nitrogen atmosphere in anautoclave for three hours at 180° C. and for three hours at 100° C. Theproduct is isolated and recrystallized from methanol.N,N'-ethylene-bisoleodiamide is obtained at a yield of 71 g and with apurity >90%.

EXAMPLE 2 Reaction of linseed oil with 1,2-diaminoethane

9 g linseed oil and 0.9 g 1,2-diaminoethane are stirred in a nitrogenatmosphere in an autoclave for three hours at 180° C. and for threehours at 100° C. The product is recrystallised from 75 ml methanol.While the amides in the mother-liquor are found to be enriched withlinoleic and linolenic acid, the amides in the recrystallized productare enriched with oleic acid, palmitic acid and stearic acid.

EXAMPLE 3 Reaction of castor oil with 1,2-diaminoethane

5.1 g castor oil and 0.5 g 1,2-diaminoethane are stirred for 5 hours inan autoclave in a nitrogen atmosphere at 120° C. The reaction product isrecrystallised from methanol. The N,N'-ethylene-bisricinoleic aciddiamide obtained in this way has a purity >90%.

(Melting point: 83°-85° C.; yield: 2.6 g)

EXAMPLE 4 Reaction of castor oil with 1,6-diaminohexane

51 g castor oil and 9.7 g 1,6-diaminohexane are stirred for 5 hoursunder nitrogen at 100° C. The reaction product is recrystallized from150 ml methanol. The hexamethylene-bisricinoleic acid diamide obtainedin this way has a purity >90%.

(Melting point: 86°-88° C. yield: 32 g)

EXAMPLE 5 Reaction of hardened castor oil with 1,2-diaminoethane

153 g hardened castor oil and 15 g 1,2-diaminoethane are stirred for 5hours in an autoclave, in a nitorgen atmosphere at 140° C. The reactionproduct is recrystallized from methanol. The bis(12-hydroxystearicacid)-N,N'-ethylenediamide obtained in this way has a purity 90%.

(Melting point: 142°-145° C.; yield: 106.5 g)

EXAMPLE 6 Reaction of hardened castor oil with 1,6-diaminohexane

5.1 g hardened castor oil and 0.97 g 1,6-diaminohexane are stirred for 5hours in an autoclave, in a nitrogen atmosphere at 150° C. The reactionproduct is subjected to hot vapour extraction with methanol. Thebis(12-hydroxystearic acid)-1,6-N,N'-hexamethylene diamide obtained inthis way has a purtiy >90%.

(Melting point: 135°-136° C.; yield: 3.7 g)

What is claimed is:
 1. A method of producing a symmetrically structured difatty acid diamide or a corresponding pure fatty acid, comprising:reacting a mixture of fatty acids or their esters with a diamine, to produce a mixture containing a symmetrical difatty acid diamide; and, separating the symmetrical difatty acid diamide from the resulting reaction mixture by recrystallization or fractured crystallization from methanol or ethanol or by hot vapor extraction with methanol based on differential solubility.
 2. The method as set forth in claim 1, wherein fats and oils are used as the fatty acids.
 3. The method as set forth in claim 1, wherein fats and oils are used as the fatty acid esters.
 4. The method as set forth in claim 1, wherein fats and oils comprising at least 50% functional fatty acids are used as the fatty acids or the fatty acid esters.
 5. The method as set forth in claim 1, wherein fats and oils comprising at least 10% extraordinary fatty acids are used as the fatty acids or the fatty acid esters.
 6. The method as set forth in claim 1 wherein euphorbia oil, high-oleic and high-linoleic sunflower oil, castor oil or hydrogenated castor oil, olive oil, linseed oil, rapeseed oil, the oil of Jatropha curcas or the oil of marine animals is used as the source of fatty acids or fatty acid esters in the reaction mixture.
 7. The method as set forth in claim 1, wherein primary and secondary aliphatic, cyclo-aliphatic, aliphatic-aromatic or aromatic diamines are used as the diamine.
 8. The method as set forth in claim 1 wherein the diamine is 1,2-diaminoethane or 1,6-diaminohexane.
 9. The method as set forth in claim 2, including a solvent is selected from the group consisting of toluene, xylene and petroleum ether.
 10. The method as set forth in claim 1 wherein the fatty acids or fatty acid esters and the diamine are reacted at a temperature between 20° C. and 300° C.
 11. The method as set forth in claim 1 wherein the mixture of fatty acids or fatty acid esters is reacted with a diamine in an inert gas atmosphere.
 12. The method as set forth in claim 1 wherein the reaction mixture additionally comprises ammonium chloride or toluene-p-sulfonic acid as a catalyst.
 13. The method as set forth in claim 1, wherein the reaction mixture additionally comprises ascorbic acid or glucose as an antioxidant.
 14. The method as set forth in claim 1, wherein the symmetrical difatty acid diamide is separated from the reaction mixture by recrystallization or fractionated crystallization from methanol or ethanol.
 15. The method as set forth in claim 1, including purifying said separated symmetrical difatty acid diamide by recrystallization.
 16. The method as set forth in claim 1, wherein said reaction mixture includes a solvent.
 17. A method of producing a symmetrically structured difatty acid, comprising:reacting a mixture of fatty acids or their esters with a diamine to produce a mixture containing a symmetrical difatty acid diamide; separating the symmetrical difatty acid diamide from the resulting reaction mixture by recrystallization or fractionated crystallization from methanol or ethanol or by hot vapor with methanol based on differential solubility; and saponifying said separated symmetrical difatty acid diamide.
 18. The method as set forth in claim 1 wherein the fatty acids or fatty acid esters and the diamine are reacted at a temperature between 50° C. and 200° C. 